If you have questions or comments, join the discussion on our LinkedIn forum.
From the 2015 UPC Illustrated Training Manual
608.2 Excessive Water Pressure.
Where static water
pressure in the water supply piping is exceeding 80 psi (552
kPa), an approved-type pressure regulator preceded by an
adequate strainer shall be installed and the static pressure
reduced to 80 psi (552 kPa) or less. Pressure regulator(s)
equal to or exceeding 1 1/2 inches (40mm) shall not require a
strainer. Such regulator(s) shall control the pressure to
water outlets in the building unless otherwise approved by
the Authority Having Jurisdiction. Each such regulator and
strainer shall be accessibly located aboveground or in a
vault equipped with a properly sized and sloped boresighted
drain to daylight, shall be protected from freezing,
and shall have the strainer readily accessible for cleaning
without removing the regulator or strainer body or disconnecting
the supply piping. Pipe size determinations shall be
based on 80 percent of the reduced pressure where using
Table 610.4. An approved expansion tank shall be installed
in the cold water distribution piping downstream of each
such regulator to prevent excessive pressure from developing
due to thermal expansion and to maintain the pressure
setting of the regulator. Expansion tanks used in potable
water systems intended to supply drinking water shall be in
accordance with NSF 61. The expansion tank shall be properly
sized and installed in accordance with the manufacturer's
installation instructions and listing. Systems
designed by registered design professionals shall be permitted
to use approved pressure relief valves in lieu of expansion
tanks provided such relief valves have a maximum
pressure relief setting of 100 psi (689 kPa) or less.
A limit of 80 psi (551.6 kPa) is the maximum
static pressure of any water supply system. The reason for
this is to reduce water hammer, unnecessary use of water,
splashing, excessive discharge of pressure relief valves and
to protect appliance and fixture valves and mechanisms
from pressure that exceeds their design limits. Any installation
with pressures above 80 psi will require a pressure regulating
valve to limit the pressure to 80 psi or below (see
By design, pressure regulating or reducing valves are
modulating valves, which have a high level of flow resistance
and consequent pressure drop through them even when
fully open. Therefore, pipe sizing downstream of the pressure
regulator must be based on "worst-case" pressure loss
during a maximum demand water flow. Worst-case pressure
loss through a listed pressure regulator is presumed to be no
greater than 20 percent; therefore, the water system is sized
based upon 80 percent of the pressure regulator’s "set" pressure,
this being a selected static pressure that is presumed
not to exceed 80 psi. Therefore, all pipe size determinations
downstream of the regulator must be based on 80 percent of
this reduced pressure when using Table 610.4.
For example, a water system has a pressure of 100 psi.
A pressure regulator will be installed and set at 80 psi. For
sizing purposes using Table 610.4, the maximum pressure
would be 64 psi, which is 80 percent of 80 psi.
The 2015 Uniform Plumbing Code Illustrated Training Manual eBook is available for purchase here.
© 2018 International Association of Plumbing and Mechanical Officials.